1. Field of the Invention
The present invention is directed to a process of fabricating a three-dimensional object from a light curable resin liquid, and more particularly to an improvement in such process for fabricating the three-dimensional object with an increased fabrication rate and accuracy.
2. Description of the Prior Art
Such three-dimensional object forming process from a light curable resin has been proposed in the art to be advantageous in fabricating a small quantity of product models or prototypes without relying upon molds or machining tools, as disclosed in Japanese Patent Early Publication [Kokai] Nos. 61-114817, and 63-141724. A process of Publication No. 61-114817 comprises to supply a light curable liquid resin into a vessel to form on a vessel bottom a liquid resin coat of a desired thickness. A laser beam is then directed from the above to move across the resulting liquid resin coat in a predetermined pattern to cure it into a correspondingly shaped cross-sectional layer. Subsequently a fresh liquid resin is supplied over the preceding cured layer and is likewise radiated to the laser beam to form another cured cross-sectional layer superimposed on the preceding cured layer. The above steps are repeated to obtain successive cross-sectional layers of cured resin which are superimposed on each other to represent a three-dimensional object of desired configuration. This process, however, poses an inherent problem that it is difficult to control exactly and rapidly the thickness of the liquid resin coat. That is, with this prior art process, the thickness of the liquid resin coat is determined by a amount of the liquid resin supplied into the vessel, but exact control of the supplying amount requires an extremely difficult measure and therefore is not available and practical at the present. Consequently, the prior art process is very likely to suffer from a thickness variation in the coat of the liquid resin and therefore eventually fails to fabricate an accurate three-dimensional object.
On the other hand, the process of another prior art Publication No. 63-141724 is free from the above problem, since it does not require to control the supplying amount of the liquid resin at the time of forming a liquid resin coat to be cured into a cross-sectional layer. As schematically shown in FIG. 32, this prior art process utilizes a vessel 210 containing a volume of the liquid resin 220 and a platform 250 which is vertically movable within the vessel 210. The platform 250 is firstly lowered sufficiently below the liquid level and is then lifted to a position immediately below the liquid level so as to obtain thereon a liquid resin coat 221 of a desired thickness, which is to be formed by exposure to a laser beam 230 into a cured cross-sectional layer 240 on the platform 250. Subsequently, the platform 250 is again immersed together with the preceding Cured layer 240 in the liquid resin 120 and is then lifted to have the top surface of the preceding cured layer 240 positioned immediately below the liquid level so as to form a fresh liquid resin coat 221 to be formed into another cured cross-sectional layer superimposed on the preceding cured layer 240. The steps are repeated to form successive cross-sectional layers 240 of cured resin on the platform 250, thereby fabricating a three-dimensional object of an intended configuration. This process relies upon a phenomenon that a fresh liquid resin supplied over the preceding cured layer 240 or the platform 250 is partially displaced outwardly as the platform 250 moves upwardly while leaving the remainder of the liquid resin remain cohered over the preceding cured layer 240, or the platform 250 due to its high viscosity, thereby providing the liquid resin coat 221 of which thickness T is determined by surface tension, viscosity and specific gravity of the liquid resin as well as interfacial tension between the liquid resin and the preceding layer 240 or the platform 250. Thus, the liquid resin coat 221 can be provided over the preceding cured layer 240 or the platform 250 in a desired thickness without the necessity of controlling the supplying amount of the liquid resin 220. With this process, however, there still remains a problem in that, as typically shown in FIG. 33 (which is a portion A of FIG. 32), when the preceding cured layer 240 is lifted just below the liquid level, the liquid resin lying over the preceding cured layer 240 will not be displaced immediately due to its high viscosity, or it is very reluctant to flow smoothly, thereby leaving a shouldered portion X on the liquid resin coat 221 which portion X is characterized to be raised relative to the surrounding liquid level. Such shouldered portion X can disappear only after an elapse of an extended time and therefore remains during the immediately following laser irradiation so that it is cured into corresponding shape which distorts the resulting layer 240 and fails to present a uniform thickness over the entire area of the cured layer 240. The distortion or uneven thickness in each cured layer will accumulate to cause a critical deformation on the successive layers, or the three-dimensional object. Although, the above problem could be avoided by sufficiently elongating the interval between the formation of the successive cross-sectional layers, this is very time-consuming and does not meet with a practical demand of efficiently fabricating the three-dimensional object. In short, the above process is not suitable to fabricate the three-dimensional object into an accurate configuration at a high production rate.